RF power amplifiers are useful components in a large variety of radio frequency (RF) electronic applications. In particular, monolithic microwave integrated circuit (MMIC) field effect transistor (FET) power amplifiers are used in low cost, high volume consumer electronics. Many of these consumer electronics are portable, small, and require very small batteries. Given very limited battery life, MMIC circuits in such products require maximum power efficiency, using the smallest and least costly battery.
Conventional MMIC power amplifier circuits are biased by using one of two techniques: fixed bias from a separate bias battery placed in series with the FET gate; or self bias developed from a resistor placed in series with the FET source. Fixed bias operation requires two separate batteries--one battery supplies positive voltage between the drain and source of a FET power amplifier and a second battery provides negative bias potential applied between the gate and source of the same FET. Conventional self-bias MMIC RF power amplifier circuits using a resistor have limited power efficiency because significant power is wasted in the resistor which subtracts from the available MMIC drain to source supply voltage.
What is needed is a technique which improves MMIC FET power efficiency and also eliminates the need for a separate battery to supply negative bias. It would also be desirable to enhance efficiency by eliminating the resistor between common ground and the source of a FET RF power amplifier to obtain self bias. Such an apparatus and method would consume less battery power and substantially increase RF power amplifier efficiency. Also, given MMICs very small size, design freedom would be gained in terms of short circuit interconnections that do not have performance degrading parasitics.